Art of drilling deep wells



Jun 3, 1941.

G. L. RA'cLn-FE ART OF DRILLING- DEEP WELLS Filed Dem-19, 1958'- 2Sheets-Sheet l June 3, '1 941' G. L. RATCLIFFE 2,244,476

ART OF DRILLING DEEP WELLS Fled D60. 19, 1938- 2v Sheets-Sheet 2lPatented June 3, 1941 UNITED STATES PATENT UFFICI?.

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George4 L. Batcliil'e, Los Angeles, Calif., assignor to National LeadCompany, Los Angeles, Calif., a corporation of New Jersey 4Claims.

This invention relat to the art of drilling deep wells and more.particularly vto the drilling of such wells through shaley formations.

In the procedure of drilling deep wells such as oil and gas 'wells therotary drilling procedure is employed. In such a .procedure 1a drillingiluid is used which is introduced through the drill stem tothe bit andthere issues to rise i-n the bore hole; from hence it is conducted to asettling ditch where the cuttingsare settled out, and then to a 'suctionpit, :from which the iluid is again conducted into'the drill stem. Insome instances the cuttings are separated from the drilling uid byscreens.

'I'he drilling uid performs various flmctions such as carrying thecuttings to .the top of the well, but a particularly useful function ofthe drilling uid is to wall the bore hole. Accordingly, the uid shouldcontain a wall-building component which, where or ry clay is used, `isthe clay itself, including its gel-forming oomponent. In many instancesa concentrated :col- .loidal clay such as bentonite is employed, asdisclosed in. the Harth .a Patent No. 1,991,637, pat- `ented February19, 1935. In some-'instances a mud weighting material-is employed,asdisclosed in the Stroud Patent No. 1,575,945, patented March 9, 1926.I.

When a drilling mud consisting of water and clay comes in contact with abed of shale as the.

well is drilled, a certain. amount of water from the drilling mud seepsinto the shale and wets it to a depth of one-fourth inch or so. Theaction of, the water varies on diiierent shales inasmuch as some shaleschip oi in small flakes when the surface becomes wet to a depth ofoneeighth or one-fourth of an inch; some shales become wet and stickyand do not slough oi and l still other sha'les disintegrate rapidly to apowdered form when they become wet'.

Applicanthas found that inthe wetted portion of shale together with anylter cake .which may have ibeen formed on the face of the shale y by thedrilling mud is placed under considerable pressure, the wettedportionwill 'be consolidated by the pressure into a hard, compact,impervious mass. The higher the pressure placed upon the shale, the morecompact will this'sheath upon the face of the shale become.

One of the objects od this invention is to sprovide a .process having`:for its purpose preventing of sloughing, caving or heaving ci shalesordinarily encountered in oil WeilV drilling; and in accordancerwiththis invention' this is accom= plished by applying suicient pressure tothe wet however, will compact shale to the point where prevents W-aterinfiltration but also mechanically A strengthens the wall of the borehole.

Another object of th-'ls invention is to provide a process in which thedrilling fluid containing a. wall-building component is subjected to apressure suilicient to compact the wallbuildingd component lon the -wallof the well.

Further objects will appear from the detailed description taken inconnection with the accompanying drawingslshowing illustrativeembodiments of this invention,` although it will 'be understood thatthis'invention is susceptible of various embodiments. y

As set forth above, some shales tend to cave or slough more readily thanother shales and it is,- therefore, diicult to state exactly whatpressure will be required to -produce the desired rev `sult inasmuch asobviouslyit would be necessary to compact a badly caving shale more thanit would be necessary tocompact a shale which had'only a tendency tocave or slough to a slight degree when wet. Generally speaking, however,ordinary clay drilling fluids have not been able to prevent the type ofheaving or sloughing to which reference has been made. The ordinary claydrilling iiuid, made up of clay land water only, would weigh sayseventy-live pounds per cubic foot or would have a specic gravity ofapproximately A1.2. The maximum weight of iluid which can be made up outof clay and water and still be utilized in drilling, is ninety pounds orless. Such a fluid would have a speciiic gravity of 1.44. An averagedrilling iiuld, therefore, let us say would have a'. speciiic gravity of1.32. If a shale Were encountered at the .bottom of a well 5,000 feetdeep in which a mud uld having a specific gravity of 1.32 was beingused. it would have a pressure on it, due to the weight of the mudcolumn, of 2,864 pounds per square inch; under the same conditions, ashale encountered at a depth of 10,000 feet would haves.

hydrostatic pressure on it, due to the weight of the mud column, of5,738 pounds persquare inch. These figures are based on. the assumptionthat no pressure exists inthe shale itself. Generally speaking, thesepressures are not sumcient to prevent the caving or sloughing to whichreference has been made. Y

Greater pressures than those mentioned above,

caving, sloughi-ng and heaving are prevented. Sometimes it is onlynecessary to slightly increase the pressure above this point butgenerally speaking, it is safer to have a substantial margin o f safetyby increasing the pressure substantially above those pressures mentionedabove. Applicant has found that this caving or sloughing will beprevented in the ordinary cases if the pressure 5 is raised to a pointwhere the pressure on the shale, expressed in pounds per square inch. is75/100 times the depth of the hole in feet. Occasi-onally this pressureis not adequate and .it

is necessary togo higher than this. In some cases it wil-l 'be advisableto have the pressure on` the shale, expressed in pounds per square inch,equivalent numerically to the depth from the surface of the ground downto the shale in feet.

In other words, in a hole 10,000 feet deep, it

. might :be necessary to have a ypressure on the shale at the bottom ofthe hole of 10,000 pounds per square inch in order to satisfactorilyconsolidate the shale and prevent heaving or caving.

Possibly, even greater pressures might have to be resorted to undercertain conditions.

These increased pressures are sometimes obtained by adding weightmaterial (consisting of .nely pulverized barytes, etc.) to the drillingmud so as to increase the weight of each unit volume of the mud therebyincreasing the hydrostatic pressure. Applicant proposes to accomplishthis by adding pressure to the drilling iluid over and above that due tothe weight of the fluid itself so' as to increase the pressure on 30 theshale to the desired point. Applicant proposes to accomplish this in twoWays:

First: By utilizing mud pumps which are capable of circulating the mudfluid at high pressures, or

Second: By utilizing a hydraulic pump at periodical intervals toincrease the pressure on the drilling fluid and thus compact the shale.`In the first embodiment of applicants :invention, if it were desired tomaintain a pressure 40 of 10,000 pounds per square in ch at the bottomof the 10,000 foot hole and the pressure on the shale dueto the weightof the drilling iiuid was 5,000 pounds per square inch, applicant wouldutilize slush pumpsfor circulating the mud which were capable of pumpingthe mud at a pressure of 5,000 pounds per square inch. This 5,000 poundsper square inch added to the 5,000 pounds' per square inch due to theweight ofl the drilling mud column would' provide the required 10,000 50pounds per square inch at the bottom of the hole after its surfacebecame wetted. In this embodiment a suitable back pressure on the muddischarged from the hole would be retained so the desired purpose wouldbe accomplished.

Practically all deep wells drilled today are equipped with suitableblow-out preventers which can be closed against the drill pipe in orderto hold any pressure encountered during drilling. 'I'hese blow-outpreventers are, customarily, only 60 used when there is danger of a wellblowing but I due to high oil, gas ork water pressures encountered indrilling. In the second embodiment of my invention the well would bedrilled in the ordinary manner with regular drilling fluid which couldconsist ofl a straight clay drilling uid or Aa clay drilling fluidweighted with barytes, iron oxide, or some other weighting material.When shale which is liabl,x to cave or sloughis encountered, it would bedrilled in the ordinary manner for a given length of time or until agiven amount of shale had been drilled. For example, say thirty feet ofshale had been drilled, circulation ofthe mud fluid would bediscontinued and a' valve placed o n the top of ,75

thel drill pipe and closed. The blow-out preventer would be closedpacking ofl the space between the casing or the wall of the hole and thedrill pipe. The hole would remain full of drilling mud. Pressure wouldthen be placed upon the column of drilling mud ythrough a pipe inlet tothe casing below the blow-out preventer. By means of a hydraulic pump,water or additional drilling mud could be pumped in on top of thedrilling mud in the well by the hydraulic pumpl until the pressure wasraised to any de- I sired point. The hydraulic pump could either belrand operated or driven in any customary manner. Care would have to beexercised not to use any more pressure than necessary due t0 the strainon the surface casing or other casing in the Well and, of course, thepressure would have to be kept below a point at which the casing wouldbe ruptured or the blow-out preventer cease to function. The desiredpressure would be maintained for a. suitable length of time, say aperiod of fifteen minutes or a half hour, until the pressure hadcompacted the wetted portion of the shale. The pressure would then bereleased and drilling would be resumed in the customary manner untilenough additional hole had been made to render it advisable to compactthe Inewly drilled shale before proceeding further.

Experience would be the only guide as to the pressure necessary in anygiven case and as to the length of time it would be necessary tomaintain the pressure in. order l to properly compact the newly wettedshale.

Pressure drilling methods are in use now but generally speaking they donot maintain more than 2,000 pounds excess pressure on the mud. Pressuredrilling is not used at present toconsolidate the shlales but only forthe purpose of 4confining oil, gas and water to their respectiveformations. In otherwords, the pressure drilling process is used toeliminate the necessity for weighted mud.

While the apparatus which may be used for performing theprocess may bevaried, for illustrative purposes, two embodiments of apparatus whichmay be employed are shown in the accompanying drawings.

Figure 1 is an elevation partly in section illustrating an apparatuscapable of carrying out the process embodying this invention; and v i,Figure 2 shows another form of apparatus. In the drawings, Figure 1shows an oil-well rig of conventional rotary type, equipped to drillunder continuous high pressure according to the disclosure of thisinvention, and Figure 2 represents the same equipped to drill underusual cfnditions with the application of intermittent high. It will beevident that a. single rig drill pipe 9; the mud owing downwardlytherethrough passes through holes in the bit III, up

around the outside of the drill pipe into the flow line II, thencethrough a ditch I2 back into the pit 2. I3 is the casing head, I4 ablowout pre- .venter of usual design, its function being to pack offaround the drill pipe, I5 a master gate valve, I6 a. rotary table forimparting rotary motion to the kelly and hence also to the bit. l1 is adraw works to operate the rotary table and operate the hoists. i

Referring to Figure 1, special features enabling the continuous highpressure method to be carried out may beseen to be as follows: Thecompounding of the pumps 3, i8 and I9 enables high mud pressures 'of5,000 to 10,000 lbs. per sq. in. to be produced. is a pressuregaugeindicating the pressure produced thereby. 2l is a packer around a kelly,a known and frequently used device to permit maintenance .of pressure inthe bore hole by preventing the, escape of l mud from the casing. Thispressure is 'also maintained by a choke 22 in the flow line. If forexample the hole is being drilled lwith 6,000

vlbs/sq. in. applied mud pressure, there will be approximately thispressure differential across both kelly packer and choke. A float valve23 is installed at the lower end of the drill string in order that newlengths of drill stem may be added while maintaining pressure in thewell. During such an operation the blowout preventer is closed aroundthe drill stem.

Referring to Figure 2, it will be seen that a three-way valve isinstalled at 24, in order that mud may be pumped either to the standpipefor routine drilling or through the feeder line 25 to the hydraulicbooster 26, this last being a device enabling mudunder very highpressure to be pumped into the space between drill pipe and casing atpoint 2l, below the blowout preventer. A pressure gauge 28 indicates theapplied pressure. In carrying out the process of the second method ofthe invention, drilling is interrupted,

the blowout preventer is closed, valve 24 is turned so that mud will befed to the booster, a valve 29 at the foot of the standpipe is closed,andI mud is pumped into the casing at 21 under any desired highpressure, usually above 5000 lbs/sq.

in.. A float valve 30 is used here also to assist valve 24 in preventingmud issuing from the drill pipe.

It is desirable to keep both the continuous and intermittent pressuresgreaterrthan the prevailing rock pressures, 'as thus caving frompressure release is prevented if the.pressure is lowered below the rockpressure. Thepressure employed is preferably at about one pound persquare inch' per 'foot of well depth... It has been foundA that in orderto preventingress of water into heaving shale, intermittent pressureshould be used for short periods of about two minutes and repeated mudthrough the final chokes so as to prevent clogging and undue wear of thechokes. An entirely closed mud system can also be used.

It will be seen that the invention accomplishes its objects. A processis provided in which sloughing, caving or heaving of shales ordinarilyencountered in oil well drilling is not only prevented, 'but the wetshale is compacted to insure consolidation of the wetted portion into arm, compact mass which not only. prevents water infiltration but alsomechanically strengthens the wall of the bore hole. This can beaccomplished in a simple and effective manner and with a minimum ofequipment. It is, of course, to be understood that this invention isapplicable not only to rotary drilling, but to cable tool drilling. Itis also applicable Ito situations where mud weightingand mudconditioning materials are employed.

It will be understood that not only is this invention susceptible ofvarious embodiments, but that various changes may be made in detailswithout departing from the spirit of this invention. It is, therefore,to be understood that this invention is not to be limited to the detailsde.- scribed and/or shown.-

Having thus described the invention, what is claimed is:

1. In the art of drilling deep wells through shaley formations, theprocess comprising, em-

ploying a drilling uid and subjecting the fluid repeatedly for shortintervals to a pressure sufficient to insure consolidation of the wettedportion of the shaley formation into a firm compact mass.

2. In the art of drilling deep wells through shaley formations, vtheprocess comprising, employinga drilling fluid and subjecting the fluidto a pressure which at any depth is substantially in excess of thatgenerated by the weight of the column of fluid at that depth in order toinsure consolidation of the wetted portion of the shaley formation intoa flrm compact mass.

3. In the art of drilling deep. wells through shaley formations-with theaid of a drilling uid, the process comprising, wetting the shale 'wall'n to a slight depth by means of Athe drilling fluid,

every half hour. Furthermore, it is desirable to r include a check valvejust above the bit in the drill pipe to retain pressure in the hole whenbreaking the kelly or when applying pressure to the mud in the casing.Snubbers may also be necessary to force the drill pipevinto the holeagainst pressure or maintain it there when pressure is momentarilyreduced. In the event of a high sand content in the mud issuing from thebore, it may be necessary to carry out 'aparltial desanding underpressure before passing the drillingl uid by applying thereto repeatedlyfor'I and compacting the drilled shale formation where it has beenwetted by applying thereto uid pressure substantially in excess of thenatural formation pressure whereby to consolidate said wetted portioninto a rm, compact mass relatively impervious to Water.

4. In the art of drilling deep wells through shaly formationswith theaid of a drilling fluid, the process comprising, compacting the drilledshale formation where it has been wetted by the short intervals, throughthe agency of the drilling fluid, fluid pressure substantially in excessof the natural formation pressure whereby to consolidate said wettedportion into a rm, compact mass relatively impervious to water.

' GEORGE L. RATCLIFFE.

